Composition of matter for and process of producing phosphate layers on iron surfaces



United States Patent COMPOSITION OF MATTER FOR AND PROCESS OF PRODUCINGPHOSPHATE LAYERS 0N IRON SURFACES Bruno Blaser, Dusseldorf-Urdenbach,Germany, assignor to Henkel & Cie. G. m. b. H., Dusseldorf-Holthausen,Germany, a corporation of Germany No Drawing. Application August 11,1953 Serial No. 373,691

Claims priority, application Germany August 14, 1952 7 Claims. (Cl.1486.15)

This invention relates to a composition of matter adapted to providearticles made of iron and parts thereof with a protective or rustproofing layer, and more particularly to a composition of matter adaptedto provide iron articles with a phosphate layer, and to a process ofproducing such phosphate layer on iron surfaces.

The practice is well known to provide iron articles and parts thereofwith a phospate layer for rust proofing said articles by treating saidarticles and parts with solutions of phosphoric acid. The adhesivenessof paints and lacquers to iron surfaces is considerably improved by suchphosphate layers. Solutions suitable for the production of such layersare prepared with free phosphoric acid as well as with acid alkaliphosphates.

When packing and shipping such free phosphoric acid or workingtherewith, there are only available containers which, on damage orbreakage, allow the phosphoric acid to run out and, thus, to causeconsiderable damage. Dry alkali salts of phosphoric acid yieldingaqueous solutions of acid reaction do not possess said disadvantage;however, the adhesiveness of lacquer and paint coatings to the ironsurfaces is not satisfactory when using such salt solutions because thesalts remain in the dry state on the treated iron surface after dryingsubsequent to the treatment.

It is, of course, possible to rinse the treated parts or articles beforedrying. This rinsing step, however, involves an additional operation andmay cause subsequent rusting of the rinsed surface. Such subsequentrusting is avoided if a small amount of the bath liquid is permitted toremain on the surface of the article during drying after the workpiecehas been removed from the bath.

It is one object of this invention to provide a new composition ofmatter adapted to provide iron articles and parts thereof with aphosphate layer which does not have the drawbacks and disadvantages ofheretofore used phosphatizing, parkerizing, and the like compositions.

Another object is to provide a rust proofing composition capable ofdepositing a phosphate layer on iron or other metal surfaces which canbe prepared and shipped as a dry powder and used in the rust proofingplant merely by the addition of water thereto.

Another object of this invention is to providea simple and effectiveprocess of producing phosphate layers on iron surfaces by means of suchnew compositions of matter.

Various other objects and advantages of this invention will becomeapparent as this description proceeds.

in principle, the present invention involves the use of aqueoussolutions prepared from addition products of phosphoric acid and amidesof low molecular carboxylic acids in the surface treatment of iron orother metal articles and parts thereof. The use of such' compositions ofmatter and solutions thereof avoids and 2,837,449 Patented June 3, 1958ice 2 eliminates the drawbacks and disadvantages of known processes,compositions and solutions.

Addition products of amides of low molecular carboxylic acids andphosphoric acid suitable for the purpose of this invention are producedin a simple manner by mixing phosphoric acid of high concentration andthe corresponding carboxylic acid amide with each other. The proportionof phosphoric acid and carboxylic acid amide in said mixture is betweenabout 1 mol to about 2 mols of amide to 1 mol of phosphoric acid.Preferably about equimolecular amounts of both components are used.Addition products obtained with an excess of phosphoric acid becomestickier and more hygroscopic with increasing excess of phosphoric acid.Therefore it is advisable to use an excess of carboxylic acid amide.This does not impair the usefulness of the resulting addition productsin the production of phosphate layers on iron surfaces. The additionproduct or adduct is immediately formed on mixing the components.Sometimes it is expedient to moderately heat the mixture to temperaturesup to about 60 C. According to a preferred mode of operation, theaddition product is formed at temperatures between 10 C. and 40 C. whilestirring the mixture. The resulting; addition products are watersoluble, solid, crystalline, pulverulent substances. The linkage betweenphosphoric acid and carboxylic acid amide, however, is not a salt-likelinkage because the pH- value of aqueous solutions of said additionproducts is not higher, or only slightly higher, than the pH-value ofequimolecular solutions of phosphoric acid whereas if the compounds, forexample of phosphoric acid and urea, were in fact salts (i. e. compoundswherein the acid hydrogen atom of phosphoric acid were neutralized) thepH-value would be considerably higher than the pH- value of anequimolecular solution of phosphoric acid.

Low molecular carboxylic acids, the amides of which, according to thisreaction, form addition products with phosphoric acid are monoanddi-basic carboxylic acids having 1 to 3 carbon atoms in their molecule.Especially suitable amides of this. type are the amides of carbonicacid, formic acid, acetic acid, propionic acid, or malonic acid. Themost important addition product for all practical purposes is theaddition product of phosphoric acid and urea.

It is advisable to subject the iron or other metal articles or partsthereof before treatment to a deg-teasing treatment. Such degreasingrnaybe effected by means of acid, neutral or alkaline baths which maycontain water soluble or water insoluble emulsified solvents. Thedegreased articles or parts thereof are treated according to thepresent-invention with solutions of said carboxylic acidamide-phosphoric acid addition products in about the same manner as withother known phosphatizing solutions. tions has proved to yield excellentresults.

The concentrationof the solution used for said treatment may bewithin'the range between 0.125% and 10.0% of phosphoruspentoxide. Thisconcentration corresponds to a concentrationof between 0.25% and 20.0%of phosphorus pentoxide, calculated for the ureaphosphoric acid additionproduct. The treatment is preferably carried outwithin a range ofconcentration of between about 0.5% and about 2.5% of phosphoruspentoxide.

about 2.0 and about 1.0. The temperature of treatment is between aboutroom temperature, i. e. about 20 C., and boiling temperature, andpreferably between about 60 C. and about C. The duration of treatmentvaries considerably. Primarily it is dependent upon the thickness ofthedesired phosphate layer, i. e., the

Working under the following special condi- Thereby the pH-value of thesolutions is between about 3.0 and'about 0.5 and preferably betweendepth to which the surface is to be phosphatized and changed. Durationof treatment is also "dependent at least to a certain extent upon:- thethickness of the work pieces to be treated; for iron" sheets and platesor thinwalled articles and parts thereof are more readily heated to therequired temperature of treatment than articles and parts of greaterwall thickness. In general, the duration of treatment will be betweenabout one-quarter of a minute and about minutes and preferably betweenabout half a minute and about 3 minutes.

It is abvisable to add water soluble organic solvents as well as acidresistant capillary active substances to the bath in order to improvewetting of the iron articles and parts with said liquid. Especiallysuitable solvents for this purpose are water soluble lower aliphaticalcohols or ketones. Capillary active substances which may besuccessfully used as additional wetting agents in the process accordingto this invention are organic compounds having in their molecule a groupwhich renders the compound water soluble, as well as a water insolublegroup. The water solubilizing group may be of acid, basic, or non-ioniccharacter. The water insoluble group is a non-aromatic, i. e. analiphatic or cycloaliphatic hydrocarbon residue with at least 8 and notmore than carbon atoms, and preferably with 12 to 18 carbon atoms in itsmolecule. As a group which renders the compound water soluble there ispreferably used a group which exhibits its solubilizing property also inacid solution such as, for instance, a sulfonic acid or a sulfuric acidmono ester group. Capillary active compounds of this type are, forinstance, fatty alcohol sulfonates, parafiin or alkyl phenyl sulfonatesand the like. In the last mentioned compounds the aromatic residuerepresents the connecting link between the alkyl residue and the watersolubilizing group.

Capillary active compounds with basic groups which render such compoundswater soluble are especially quaternary ammonium compounds, such as, forinstance, alkyl pyridium salts with 8 to 14 carbon atoms in the alkylresidue, or alkyl trimethyl ammonium salts in which the alkyl residue isa higher molecular residue, i. e. contains the above mentioned number ofcarbon atoms. Especially noteworthy compounds of the group of capillaryactive compounds with non-ionic, water solubilizing groups are capillaryactive compounds with polyglycol ether chains. They may be derived fromfatty acids, fatty acid amides, fatty alcohols, alkyl phenols, alkylsulfonam-ides, or alkyl phenyl sulfonamides. The use of such additionsis recommended especially when iron articles or parts are to be treatedvwhich are relatively clean or are only slightly soiled so thatcontamination of the surface may be removed by the phosphatizing bathitself.

The addition products of phosphoric acid suitable for carrying out theprocess according to this invention can be readily handled and workedwith since they are solid, pulverulent products. They can be mixed withwetting agents or emulsifiers for simultaneous use therewith and may bemarketed in such mixture as solid, pulverulent products which are freeof the disadvantages of rust proofing preparations using liquidphosphoric acid. When used to produce phosphate layers on iron or othermetals, for instance, urea phosphate dried on said treated ironsurfacedoes not impair the adhesiveness of subsequent paint or lacquer coatingapplied to such treated surface, as is the case when using alkaliphosphates. Therefore the liquid fromthe treatment bath remaining on thetreated surface need not be rinsed off after treatment, thuseliminatingone operation in the working up of the treated articles .orparts.

The phosphoric acid amide addition products for use according to myinvention may be prepared in various ways by the simple mixture of thephosphoric acid and an amide of a low molecular carboxylic acid. Someexamples of methods of preparation which may be used are as follows:

Example 1 addition product or adduct, which may be added to water toprovide a rust proofing bath.

Example 2 100 grams of phosphoric acid (76%) are mixed with 63 grams ofphosphorus pentoxide and kept from one to two days at room temperature.100 grams of urea dissolved in a small amount of methanol are added to'the solution. After the heat of reaction has been dissipated, the ureaaddition product crystallizes in fine crystals. Crystallization may beimproved by cooling rapidly to a lower temperature. After filtration afinely crystallized urea addition product of great purity is recovered.The methanol which still contains a small amount of said additionproduct may serve as a solvent for the next batch.

Example 3 142 grams of phosphorus pentoxide are carefully added to 54grams of water. The mixture is then heated on a steam bath for severalhours. The cool hydrolysate is then mixed with 120 grams acetamidewhereby the temperature of the reaction mixture increases. A clearsolution results which, on cooling, solidifies to a crystalline additionproduct or adduct suitable for the production of treatment baths for theformation of protective layers on iron or other metal articles.

Example 4 142 grams of phosphorus pentoxide are carefully added to 54grams of water. The mixture is heated on a steam bath for several hours.The cooled hydrolysate is then mixed with a solution of 90 grams offormamicle dissolved in cc. of methanol. After the heat of reaction hasbeen dissipated, a colorless addition product crystallizes which isfiltered ofi. The mother liquor may be used as solvent for the nextbatch.

The following examples serve to illustratethe application of theproducts of my invention to the treatment of metal articles without,however, limiting the same thereto.

Example 5 Several cold rolled iron sheets of the size 50 mm. by 150 mm.and 30 mm. by 15% mm. and the thickness of 0.6 mm. were dcgrcased bymeans of an alkaline bath, thoroughly rinsed with water, and then placedfor 3 minutes into a phosphoric acid solution heated to C. andcontaining 0.72% of phosphorus pentoxiclc. One of the two solutions usedin this comparative test was prepared from monobasic sodium phosphateand had a pH of 4.5; the other solution was made from a phosphoricacid-urea addition product or adduct and had a pH of 1.6-1.8. Thetreated sheets were removed from the bath and immediately thereafterdried in a drying oven at C. The dried sheets, after cooling, wereimmersed in a black nitrocellulose lacquer. Untreated sheets as controlswere lacquered in the same way. The nitrocellulose lacquer used wasdiluted with solvents in order to adjust its viscosity to a time ofefrlux of 35 to 36 seconds in a Ford beaker. Such a lacquer layer isvery sensitive to cracking and peeling in the subsequent shaping andworking of the treated workpieces. After said lacquering, the sheetsremained first in the workrom for 48 hours and were then exposed forweathering to the open air for 4 days.

The lacquer layer on the various test sheets was tested for its bendingand impact resistance.

In the bending.

test the 30 mm. by 150 mm. sheets were bent about 180 around a 7 mm.mandrel. The untreated sheets and the sheets treated with monobasicsodium phosphate showed in the bending test considerable breaking andpeeling of the lacquer layer. Sheets treated with the solution of aphosphoric acid-urea addition product did not exhibit any noticeablepeeling of the lacquer layer.

Impact tests were carried out on the 50 mm. by 150 mm. test sheets withthe device described in the journal, Farben, Lacke, Anstrichstofie(Pigments, Lacquers and Paints) year 1949, page 10. The impactresistance of the lacquer was observed, however, not electrically butvisually. The drop weight, weighing 2 kg., was allowed to drop upon the50 mm. by 150 mm. sheet to be tested from a height of 40, 50, 60, 70,80, and 90 cm. In these tests the lacquer layer of the untreated sheetscracked off at all heights of dropping. No cracking oiT of the lacquerwas observed with sheets treated with monobasic sodium phosphate atdrops of 40 cm. and 50 cm. while at drops of between 60 cm. and 90 cm.the lacquer cracked off. The sheets treated with a solution of thephosphoric acid-urea addition product or adduct did not show anycracking of the lacquer at any of the heights from which the weight wasdropped.

Example 6 A pulverulent product for carrying out the process accordingto this invention may consist of 6% of urea phosphate adduct and 3% ofan alkyl phenyl sulfonate with 10 to carbon atoms in its alkyl residue.The alkyl phenyl sulfonate may be substituted in said powder by the sameamount of a fatty alcohol sulfonate having 12 to 14 carbon atoms in itsalkyl residue or by the same amount of an addition product of about 8mols of ethylene oxide to such a fatty alcohol. The same amount of analkyl pyridium chloride obtained by condensing a mixture of alkylchlorides having 8 to 14 carbon atoms in their alkyl residue andpyridine may also be used in place of said alkyl phenyl sulfonate. Anyof these products or mixtures thereof may be added to water to provide atreatment bath for coating or rust proofing iron or other metalarticles.

The treatment of iron articles in the above described phosphatizing bathmay be carried out under the same conditions as described in Example 5,or under the usual conditions of phosphatizing or rust proofing iron orsteel articles.

In place of the addition product of phosphoric acid and urea used in theabove examples, and which are the most important from a practicalstandpoint, there may be employed other addition products of phosphoricacid and other acid amides such as, for instead, formamide,

acetamide, oxamide, malonamide, and other amides of monoand di-basiccarboxylic acids having 1 to 3 carbon atoms in their molecule.

Various changes and modifications in the composition of the phosphoricacid addition products, the con-' centration of the phosphatizing bath,the temperature and duration of treatment, and the like, may be made bythose skilled in the art in accordance with the principles set forthherein within the spirit of my invention and the scope of the followingclaims.

I claim:

1. In a process of producing phosphate layers on iron surfaces, the stepcomprising immersing iron articles in an aqueous phosphatizing solutionconsisting essentially of the addition product of phosphoric acid and anamide of a low molecular carboxylic acid containing from 1 to 3 carbonatoms to cause formation of a phosphate layer on the surface of saidiron article.

2. In a process of producing phosphate layers on iron surfaces accordingto claim 1, wherein the amide of a low molecular carboxylic acid isurea.

3. In a process of producing phosphate layers on iron surfaces accordingto claim 1, wherein the pH of the aqueous phosphatizing solution, duringtreatment, is between 05 and 3.0.

4. In a process of producing phosphate layers on iron surfaces accordingto claim 3, wherein the pH of the aqueous phosphatizing solution, duringtreatment, is between 1.0 and 2.0.

5. In a process of producing phosphate layers on iron surfaces accordingto claim 1, wherein the temperature of the aqueous phosphatizingsolution, during treatment, is between about 20 C. and about boilingtemperature.

6. In a process of producing phosphate layers on iron surfaces accordingto claim 5, wherein the temperature of the aqueous phosphatizingsolution, during treatment, is between about C. and C.

7. In a process of producing phosphate layers on iron surfaces accordingto claim 1, wherein the aqueous phosphatizing solution contains betweenabout 0.125% and about 10.0% of phosphorus pentoxide.

References Cited in the file of this patent UNITED STATES PATENTS1,428,087 Gravell Sept. 5, 1922 1,440,056 Clarkson et al Dec. 26, 19221,936,533 Albrecht Nov. 21, 1933 1,951,518 Meisner et a1. Mar. 20, 19342,318,606 Goebel May 11, 1943 2,476,345 Zavarella July 19, 19492,481,977 Cinamon Sept. 13, 1949 2,715,059 Miller Aug. 9, 1955

1. IN A PROCESS OF PRODUCING PHOSPHATE LAYERS ON IRON SURFACES, THE STEP COMPRISING IMMERSING IRON ARTICLES IN AN AQUEOUS PHOSPHATIZING SOLUTION CONSISTING ESSENTIALLY OF THE ADDITION PRODUCT OF PHOSPHORIC ACID AND AN AMIDE OF A LOW MOLECULAR CARBOXYLIC ACID CONTAINING FROM 1 TO 3 CARBON ATOMS TO CAUSE FORMATION OF A PHOSPHATE LAYER ON THE SURFACE OF SAID IRON ARTICLE. 